Two of the biggest problems with conventional herbicides and insecticides are the off-target effects they cause and the development of resistance to the chemical as a result of prolonged and sustained use.

Due to its specificity, RNAi sprays allow farmers to get around the first issue, but resistance will remain an issue of the technology is overused, according to scientists.

Cornell University professor of entomology, Dr Jeffery Scott, said under the right conditions the technology could be "revolutionary''.

"Let's say you've got a crop being affected by two different pests: Colorado Potato Beetle and one other," he hypothesized.

"This technology lets you customise a control for the beetle, and leave the other pest alone."

But he warned that specificity came down to choose the right genes to target, and to this end scientists have been able to use genomics databases to find target genes.

But for plants, other scientists are not convinced the technology is advanced enough to be an effective weed killer.

Dr Stephen Powles from the Australian Herbicide Resistance Initiative at the University of Western Australia said it is difficult for large, foreign molecules, like RNA, to penetrate the leaf cuticle.

Further, to be effective it has to do that quickly, because sunlight will degrade the molecules.

"It's an alluring possibility, and there's no doubt that Monsanto and various start-up companies are active in spray applied RNAi technology," he said.

Regulation barriers

RNAi sprays would be a form of genetic control, but still considered an insecticide in the United States, according to Dr Scott.

Therefore the U.S. Environmental Protection Agency could be responsible for regulating its use.

But whether to regulate all RNAi sprays in one pass, or seek approval for each, targeted RNAi is another question but Dr Scott said regulators will not have to deal with that for some time, as the technology is still in the very early stages.

There is also the question of whether the technology falls under "genetic modification" or not.

Dr Stephen Powles favours the latter interpretation.

"It is not a genetically modified organism, it is a piece of double stranded RNA, so I can appreciate the arguments that it should not be called GM."